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Date: Sun, 24 Jul 2011 02:05:13 +0200 (CEST) From: Thomas Gleixner <tglx@...utronix.de> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, laijs@...fujitsu.com, darren@...art.com, rostedt@...dmis.org, mingo@...e.hu, linux-kernel@...r.kernel.org Subject: Re: [PATCH RFC] rtmutex: Permit rt_mutex_unlock() to be invoked with irqs disabled On Sun, 24 Jul 2011, Thomas Gleixner wrote: > On Sat, 23 Jul 2011, Paul E. McKenney wrote: > > > On Thu, Jul 21, 2011 at 01:32:48PM +0200, Peter Zijlstra wrote: > > > On Tue, 2011-07-19 at 13:14 -0700, Paul E. McKenney wrote: > > > > Because rcu_read_unlock() can be invoked with interrupts disabled, it can > > > > in turn invoke rt_mutex_unlock() with interrupts disabled. This situation > > > > results in lockdep splats (https://lkml.org/lkml/2011/7/7/362) because the > > > > rt_mutex structure's ->lock_wait is acquired elsewhere without disabling > > > > interrupts, which can result in deadlocks. > > > > > > > > This commit therefore changes the rt_mutex structure's ->lock_wait > > > > acquisitions to disable interrupts. > > > > > > > > An alternative fix is to prohibit invoking rcu_read_unlock() with > > > > interrupts disabled unless the entire preceding RCU read-side critical > > > > section has run with interrupts disabled. However, there is already > > > > at least one case in mainline where this potential rule is violated, > > > > and there might well be many more. These would likely be found one at > > > > a time using the lockdep-water-torture method, hence the alternative > > > > fix in the form of this commit. > > > > > > Thomas, I'm inclined to merge this, any objections? > > > > FWIW, it has been passing tests here. > > If it's only the unlock path, I'm fine with that change. > > Acked-by-me Hrmpft. That's requiring all places to take the lock irq safe. Not really amused. For -RT that's a hotpath and we can really do without the irq fiddling there. That needs a bit more thought. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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